A number of polyunsaturated fatty acids (PUFA) are either essential for a normal development of the human body or potential prophylactic/therapeutic agents for atherosclerosis, rheumatoid arthritis, carcinogenesis, type I diabetes, premature birth and low birth-weight, and abnormal development of the CNS and visual acuity in newborns. 13C-Labeled PUFA are of interest for metabolic and in vivo 13C NMR studies, and clinical CO(2)-13 breath-test for fat malabsorption. Phase I proposes to synthesize some key labeled intermediates, including propargyl-1,3-13(C)2 and propargyl-2-13C alcohols, that are necessary for the synthesis of PUFA 13C-labeled at alternating carbons. Phase II may complete the syntheses of the labeled intermediates and assemble them following generally known methodologies to produce the labeled PUFA.